void LoadFlowDocumentPageViewerWithXAMLFile(string fileName)
{
// Open the file that contains the FlowDocument...
FileStream xamlFile = new FileStream(fileName, FileMode.Open, FileAccess.Read);
// and parse the file with the XamlReader.Load method.
FlowDocument content = XamlReader.Load(xamlFile) as FlowDocument;
// Finally, set the Document property to the FlowDocument object that was // parsed from the input file.
flowDocPageViewer.Document = content;
xamlFile.Close();
}

If the FlowDocument references external resources (such as image files) using relative uniform resource identifiers (URIs), it is necessary to specify a ParserContext that includes a BaseUri so that the parser can make sense of the relative URIs. The XamlReader class provides Load method that accepts a ParserContext.